2017 Duramax Dyno Numbers

jfritz_drfritz wrote:

4x4ord wrote:

Grit dog wrote:
And one can pick apart dynos as well. 2 dynos, different conditions, etc, etc,etc.
Either way, we all know there's more than a 4% loss from crank to pavement.
So either, it's a rigged test ( we can open the popcorn bar up on that one) or GM was/is conservative in their ratings and that Dmax is a powerhouse!

I take it you come up with the 4% drive loss by using the 880 lb ft mentioned in the video and the 910 lbft that GM rates the truck at. So if we agree 4% is impossible and assuming an unlikely driveline loss of only 12%, then either the new Duramax is making at least 1000 lbft of torque and GM has decided to be conservative on their numbers and rate the new engine at 910 lbft or the test is rigged.

I think there is a most likely third option: That the 880 lb ft of torque is not meant to represent the engine torque less driveline loss but rather it is the torque measured on the dyno rollers.

I think you probably know this. A chassis Dyno measures the rate of acceleration of a known rotating mass. The torque and horsepower therefore are mathematical calculations. The raw results then are a measure of rear wheel horsepower. Correction factors for altitude and temperature are applied afterwards. Generally on inertial (not a load step dyno) you try to get as close to 1:1 gear ratio as possible (most efficient). An operator can manipulate the data several ways (gear ratio, correction factors, engine temp, standards). Back to back tests on the SAME dyno can be meaningful, tests on different dynos much less so.

Now that you mention it, I should have known that most chassis dynos are inertia based and derive their results from measuring the rate of acceleration of a known rotating mass. I honestly don't know much about chassis dynos so it is just common sense that is causing me to question the results shown on the video. I suppose the guys at TFL Truck will not be willing to put 30,000 lbs behind the Duramax on account that being more than GM's tow rating allow for. Maybe some Colorado potato farmer will have to make a you tube video for us.